Consumers often prefer to cook food in a microwave oven rather than conventional ovens because of the reduced cooking time required to heat foods in a microwave oven. As a result, a wide variety of food items have been designed for heating in a microwave oven. Popular examples of these items include lasagna, cheese macaroni dishes and vegetable casseroles.
Microwave ovens do not transfer heat to a material in the same manner as conventional ovens. Rather, the material is induced to heat itself as the microwave oven generates a continually changing electrical field. Accordingly, microwave cooking requires containers that are transparent to microwave energy.
A variety of trays and containers have been developed specifically for microwave heating. For example, Matsui U.S. Pat. No. 4,704,510 discloses a container for food service which is adapted to withstand heating in a microwave oven. The container is formed from a laminate sheet material consisting of a non-stretched polyethylene terephthalate film laminated to the interior of a foamed plastic sheet. The bottom of the container is raised to curve concavely towards the center thereof to distribute the container contents and improve upon the heat distribution within the container during the heating or cooking of the contents with microwave radiation. However, the laminated container material utilized is relatively expensive to construct.
Bowen, et al. U.S. Pat. No. 4,486,640 relates to a utensil for cooking and/or baking foods in a microwave oven in which a generally flat-bottomed container base incorporates a removable tray and a closure lid possessing apertures to enable the escape of steam which is generated during cooking. This microwaveable container structure is relatively complex and expensive, while not facilitating the optimum distribution of foods or comestibles within the container to allow for a more uniform temperature distribution therethrough during cooking with microwave energy.
Watkins U.S. Pat. No. 4,416,906 discloses a microwave food heating container having a central raised core in the container bottom to essentially distribute the food contained therein about an annulus to improve upon the uniform heating thereof. As in the other above-mentioned patents, there is no optimum distribution of the food within the container so as to allow for a greater efficiency during cooking and a degree in the uniformity of the temperature which will meet the demands of the technology for cooking with microwave energy.
Isakson, et al. U.S. Pat. No. 4,640,838 describes a vapor-tight microwave oven package incorporating a vent enabling the escape of steam or vapor which is generated during cooking, and does not provide for an optimum distribution of foods within a generally rigid microwaveable container to attain uniform temperatures during microwave cooking or heating of the food contents of a container.
Levendusky, et al. U.S. Pat. No. 4,560,850 discloses a microwave container with a cover incorporating a port for the release of steam, and with a raised container bottom to distribute the foods therein for more even cooking or heating. This structure also fails to provide for the optimum dispersion of a food within a specially configured container and does not allow for an adequately uniform temperature distribution through the food as it is cooked by microwave energy with a resultant higher degree of efficiency.
Although various measures have been undertaken to improve upon efficiency and temperature uniformity of microwave cooking, they have not proven to be entirely adequate, especially when used for prepackaged, single-serve applications. Many single-serve microwavable trays are relatively flimsy, making it difficult for a consumer to remove a tray containing hot items from the microwave without experiencing some discomfort. Moreover, many prior art trays require expensive container constructions.
Single-serve containers often require specially designed wrappers or packaging cartons to display nutritional information, ingredients, and heating instructions. These wrappers and packaging cartons can become destroyed or separated from the carton upon use, requiring separate packaging materials and instructions for each microwave serving. This extraneous packaging material increases the cost to the consumer. Prior art trays also incorporate inefficient designs which do not adequately utilize the retail shelf space or the volume of the shipping cube.